Large roller bearings, in the sense of the present invention, are roller bearings which have axial bearing races or radial bearing races and which are formed with bearing rings provided with such races and which can be mounted in bearing assemblies, usually with bearing housings which are attached by bolts or otherwise assembled to a particular structure and can have multiple bearing rings, multiple bearing races, bearing rings juxtaposed with other bearing rings such that either may be an inner ring and the other an outer ring, systems which are assembled together so that multiple rows of balls or rollers are provided on the races and bearing rings which are of a wide variety of configurations.
In general, the bearing rings which are fabricated for such purposes are machined so as to have an axial bore, the races themselves are finished following machining operations and the bearing ring can then be hardened. The bearing rings can be formed as nose rings, support rings, holder rings, disk like axial-race rings and the like.
An axial bearing race, for the purposes of the present invention will be understood to be a race which presses axially upon an array of rollers at least in part or against which an array of rollers press axially. Correspondingly, a radial bearing race is a race which can take up or apply a supporting force in a radial direction.
Large roller bearings in general, depending upon the configuration, can have one, two or more pairs of races between which respective roller arrays are provided and one, two or more bearing rings provided with these races, fabricated by machining and then hardened.
In conventional processes for fabricating bearing rings for such large roller bearings, the hardening can be effected by an inductive heating and a shower type quenching system. The inductive hardening is effected as a feed hardening in which the inductor is held in place and conforms to the contour or the race of the bearing ring and the bearing ring is continuously advanced relative to the inductor and the quenching shower so that each segment of the bering race is heated and quenched in a progressive and continuous manner. An advantage of this system is that it allows the races of bearing rings of practically any size to be hardened.
A drawback, however, is that it is not possible to be absolutely certain that all parts of the bearing race will be uniformly hardened and hence at the conclusion of the hardening there can be incompletely hardened segments and segments which remain soft and thus significantly reduce the life of the bearing and the properties thereof.
The defects in continuous hardening as practiced in these earlier systems appear to derive from some slippage in the combined heating and quenching of the workpiece as practiced segment wise around the bearing ring as the latter is rotated past the inductor and the quenching spread.
It is also known to heat the bearing race of a bearing ring for a large roller bearing with an oxyacetylene flame and then to quench the bearing ring in an oil or emulsion bath. With this so-called flame hardening, a plurality of burners are uniformly distributed around the periphery of the bearing ring and juxtaposed with the bearing race to be hardened. The bearing ring is rotated about an axis which as a rule can be a vertical axis perpendicular to the plane of the bearing race so as to attempt to distribute the heating from the oxyacetylene torches uniformly over the periphery of the entire bearing ring. Immediately upon attainment of the predetermined hardening temperature for the race to be hardened, the burners are shut down and the bearing ring is immersed in the oil bath or the emulsion both for quenching. This system has a significant drawback in that it poses dangers to personnel who must handle the bearing ring and carry out the operations because of the need to manipulate explosive gas mixtures and because of significant fume development. Furthermore, the heating process can only be controlled to a limited extent so that the strength properties of the product may be limited at least in part. More particularly, it is observed that there are races which are formed which have a lesser hardness than is desired and a larger grain structure in the hardened race which can reduce the life of the fabricated bearing.
In a Japanese Patent Application Publication under number Sho 60-141827, a process has been described for producing a bearing race with a hardened surface layer in a groove like recess in a bearing ring in which the hardening surface layer is formed by rotating a cylinder element containing the bearing race about its axis, heating it with an electromagnetic field from at least one inductor simultaneously with the rotation while maintaining a spacing between the inductor and the bearing race and then quenching the bearing race by spraying it with a coolant following the heating operation.
This process, in which a constant gap is provided between the bearing race and the inductor allows an intensive application of heat at the bearing race portion juxtaposed with the inductor.
However, it has been discovered that simply by carrying out a heating in this manner, it is not possible to reliably harden bearing races in a controlled manner for bearing rings for large bearings.